1. Field of the Invention
The invention relates to a flat lighting device to be used as a back light for a liquid crystal display to be suitably used for an apparatus for a display device of a portable or automobile mounted television receiver or a portable personal computer or the like.
2. Background Art
FIG. 6 shows an example of the constitution of the above-described type of conventional flat lighting device 90. The flat lighting device 90 is constituted by a light transmission member 91 formed by transparent material having a high refractive index such as methacrylic resin, a light source 92 such as a cold cathode fluorescent lamp and a reflecting mirror 93 covering said light source 92.
The front side of said light transmission member 91 functions as a luminous surface 91a with the area approximately equal to the area of the display space of a liquid crystal display 81 for lighting, and on a reflection surface 91b which is the rear side of the luminous surface 91a, for example a dotted reflecting pattern 94 is formed by white ink.
The lateral side of said light transmission member 91 formed approximately perpendicularly to the luminous surface 91a functions as an incident surface 91c, the above-described light source 92 is confronted with the incident surface 91c, and a reflecting mirror 93 for reflecting light emitted from the light source 92 and advancing in the direction other than the incident surface 91c toward the incident surface 91c is attached utilizing the thickness of the light transmission member.
Therefore, in the conventional flat lighting device 90, said light transmission member 91 is basically formed in the shape of a rectangular parallelepiped or a thick plate. A diffusion plate 82, for example milky for diffusing light is provided between said luminous surface 91a and the liquid crystal display 81 for removing unevenness of light. A reflecting plate 83, for example formed by a mirror is provided at the rear of said reflecting pattern 94 on the side of the reflection surface 91b for preventing light from being lost through the reflection surface 91b.
However, in the above-described conventional flat lighting device 90, the width W1 of the flat lighting device 90 when said light source 92 and the reflecting mirror 93 are attached in the vicinity of the incident surface 91c is wider than the width W2 of the liquid crystal display 81 because said light transmission member 91 is formed in the shape of a rectangular parallelepiped. Therefore the frame around the display area is large compared with the display area when the flat lighting device and the liquid crystal display are integrated in a case and form, for example a display of a portable television, which causes the entire display to be large and solution of such a problem is desired.